Fuel for fuel cell system

ABSTRACT

A fuel for a fuel cell system, which comprises at least 5 vol. % of hydrocarbons based on the whole fuel and 0.5 to 20 mass % of oxygenates in terms of an oxygen content based on the whole fuel, wherein the total content of hydrocarbon compounds which have carbon numbers of 7 and 8 is 20 vol. % or more based on the whole hydrocarbons and the total content of hydrocarbon compounds which have carbon numbers of 10 or more is 20 vol. % or less based on the whole hydrocarbons, and a fuel for a fuel cell system, which comprises at least 5 vol. % of hydrocarbons based on the whole fuel and 0.5 to 20 mass % of oxygenates in terms of an oxygen content based on the whole fuel, wherein the fuel has distillation properties; the initial boiling point in distillation of over 40° C. and 100° C. or lower, the 10 vol. % distillation temperature of over 50° C. and 120° C. or lower, the 90 vol. % distillation temperature of 110° C. or higher and 180° C. or lower, and the final boiling point in distillation of 130° C. or higher and 210° C. or lower. The fuel for a fuel cell system has a high power generation quantity per weight, a high power generation quantity per CO 2  emission, a low fuel consumption, a small quantity of evaporative gas (evapo-emission), small deterioration of a fuel cell system comprising such as a reforming catalyst, a water gas shift reaction catalyst, a carbon monoxide removal catalyst, fuel cell stacks and the like to maintain the initial performances for a long duration, good handling properties in view of storage stability and inflammability, and a low preheating energy.

TECHNICAL FIELD

The present invention relates to a fuel to be used for a fuel cell system.

BACKGROUND ART

Recently, with increasing awareness of the critical situation of future global environments, it has been highly expected to develop an energy supply system harmless to the global environments. Especially urgently required are to reduce CO₂ to prevent global warming and reduce harmful emissions such as THC (unreacted hydrocarbons in an exhaust gas), NO_(x), PM (particulate matter in an exhaust gas: soot, unburned high boiling point and high molecular weight fuel and lubricating oil). Practical examples of such a system are an automotive power system to replace a conventional Otto/Diesel engine and a power generation system to replace thermal power generation.

Hence, a fuel cell, which has high energy efficiency and emits only H₂O and CO₂, has been regarded as a most expectative system to respond to social requests. In order to achieve such a system, it is necessary to develop not only the hardware but also the optimum fuel.

Conventionally, as a fuel for a fuel cell system, hydrogen, methanol, and hydrocarbons have been candidates.

As a fuel for a fuel cell system, hydrogen is advantageous in a point that it does not require a reformer, however, because of a gas phase at a normal temperature, it has difficulties in storage and loading in a vehicle and special facilities are required for its supply. Further, the risk of inflammation is high and therefore, it has to be handled carefully.

On the other hand, methanol is advantageous in a point that it is relatively easy to reform, however power generation quantity per weight is low and owing to its toxicity, handling has to be careful. Further, it has a corrosive property, special facilities are required for its storage and supply.

Like this, a fuel to sufficiently utilize the performances of a fuel cell system has not yet been developed. Especially, as a fuel for a fuel cell system, the following are required: power generation quantity per weight is high; power generation quantity per CO₂ emission is high; a fuel consumption is low in a fuel cell system as a whole; an evaporative gas (evapo-emission) is a little; deterioration of a fuel cell system comprising such as a reforming catalyst, a water gas shift reaction catalyst, a carbon monoxide conversion catalyst, fuel cell stacks and the like is scarce to keep the initial performances for a long duration; a starting time for the system is short; and storage stability and handling easiness are excellent.

Incidentally, in a fuel cell system, it is required to keep a fuel and a reforming catalyst at a proper temperature, the net power generation quantity of the entire fuel cell system is equivalent to the value calculated by subtracting the energy necessary for keeping the temperature (the energy for keeping balance endothermic and exothermic reaction following the preheating energy) from the actual power generation quantity. Consequently, if the temperature for the reforming is lower, the energy for preheating is low and that is therefore advantageous and further the system starting time is advantageously shortened. In addition, it is also necessary that the energy for preheating per fuel weight is low. If the preheating is insufficient, unreacted hydrocarbon (THC) in an exhaust gas increases and it results in not only decrease of the power generation quantity per weight but also possibility of becoming causes of air pollution. To say conversely, when some kind of fuels are reformed by the same reformer and the same temperature, it is more advantageous that THC in an exhaust gas is lower and the conversion efficiency to hydrogen is higher.

The present invention, taking such situation into consideration, aims to provide a fuel suitable for a fuel cell system satisfying the above-described requirements in good balance.

DISCLOSURE OF THE INVENTION

Inventors of the present invention have extensively investigated to solve the above-described problems and found that a fuel comprising oxygenates (oxygen-containing compounds) in the specific amount is suitable for a fuel cell system.

That is, the fuel for a fuel cell system according to the first aspect of the present invention is:

-   (1) a fuel for a fuel cell system, which comprises at least 5 vol. %     of hydrocarbons based on the whole fuel and 0.5 to 20 mass % of     oxygenates in terms of an oxygen content based on the whole fuel,     wherein the total content of hydrocarbon compounds which have carbon     numbers of 7 and 8 is 20 vol. % or more based on the whole     hydrocarbons and the total content of hydrocarbon compounds which     have carbon numbers of 10 or more is 20 vol. % or less based on the     whole hydrocarbons.

The fuel for a fuel cell system according to the second aspect of the present invention is:

-   (2) a fuel for a fuel cell system, which comprises at least 5 vol. %     of hydrocarbons based on the whole fuel and 0.5 to 20 mass % of     oxygenates in terms of an oxygen content based on the whole fuel,     wherein the fuel has distillation properties; the initial boiling     point in distillation of over 40° C. and 100° C. or lower, the 10     vol. % distillation temperature of over 50° C. and 120° C. or lower,     the 90 vol. % distillation temperature of 110° C. or higher and     180° C. or lower, and the final boiling point in distillation of     130° C. or higher and 210° C. or lower.

The fuel for a fuel cell system, which comprises said oxygenates in the specific amount, is preferable to satisfy the following additional requirements:

-   (3) sulfur content is 50 ppm by mass or less based on the whole     fuel; -   (4) saturates are 30 vol. % or more based on the whole hydrocarbons; -   (5) olefins are 35 vol. % or less based on the whole hydrocarbons; -   (6) aromatics are 50 vol. % or less based on the whole hydrocarbons; -   (7) ratio of paraffins in saturates is 60 vol. % or more; -   (8) ratio of branched paraffins in paraffins is 30 vol. % or more; -   (9) heat capacity of the fuel is 2.6 kJ/kg 0° C. or less at 15° C.     and 1 atm in liquid phase; -   (10) heat of vaporization is 400 kJ/kg or less; -   (11) Reid vapor pressure is 10 kPa or more and less than 100 kPa; -   (12) research octane number is 101.0 or less; -   (13) oxidation stability is 240 minutes or longer; and -   (14) density is 0.78 g/cm³ or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of a steam reforming type fuel cell system employed for evaluation of a fuel for a fuel cell system of the invention.

FIG. 2 is a flow chart of a partial oxidation type fuel cell system employed for evaluation of a fuel for a fuel cell system of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the contents of the invention will be described further in detail.

In the present invention, it is necessary that the content of hydrocarbons is at least 5 vol. % based on the whole fuel because the fuel comprising said content of hydrocarbons shows a high power generation quantity per weight and a high power generation quantity per CO₂ emission.

In the present invention, oxygenates indicate alcohols having carbon numbers of 2 to 4, ethers having carbon numbers of 2 to 8 and the like. The oxygenates include methanol, ethanol, dimethyl ether, methyl-tert-butyl ether (MTBE), ethyl-tert-butyl ether, tert-amyl methyl ether (TAME), tert-amyl ethyl ether and the like.

It is necessary that the content of the oxygenates is 0.5 mass % or more in terms of an oxygen content based on the whole fuel in view of a low fuel consumption of a fuel cell system as a whole, a low THC in an exhaust gas, short starting time of a system and that the content of the oxygenates is 20 mass % or less, most preferably 3 mass % or less in view of the balance to a high power generation quantity per weight, a high power generation quantity per CO₂ emission.

In the first aspect of the present invention, the content of hydrocarbon compounds having carbon numbers of 7 and 8 in total (V (C₇+C₈)) shows the content of hydrocarbon compounds having 7 carbon atoms and 8 carbon atoms in total on the bases of the whole hydrocarbons and is required to be 20 vol. % or more in view of a high power generation quantity per weight, a high power generation quantity per CO₂ emission, and a low fuel consumption of a fuel cell system as a whole and preferably 25 vol. % or more, more preferably 30 vol. % or more, further more preferably 35 vol. % or more, and most preferably 40 vol. % or more.

In the first aspect of the invention, in view of a high power generation quantity per CO₂ emission, a low fuel consumption of a fuel cell system as a whole, and small deterioration of a reforming catalyst to maintain initial performances for a long duration, the total content of hydrocarbon compounds having carbon numbers of 10 or more (V (C₁₀₊)) on the bases of the whole hydrocarbons is preferably 20 vol. % or less, more preferably 10 vol. % or less, and most preferably 5 vol. % or less.

The content of hydrocarbon compounds having a carbon number of 4 is not particularly limited, however, the content of hydrocarbon compounds having a carbon number of 4 based on the whole hydrocarbons (V (C₄)) is preferably 15 vol. % or less since the evaporative gas (evapo-emission) can be suppressed to low and the handling property is good in view of inflammability or the like and more preferably 10 vol. % or less and further more preferably 5 vol. % or less.

The content of hydrocarbon compounds having a carbon number of 5 is not particularly limited, however, the content of hydrocarbon compounds having a carbon number of 5 based on the whole hydrocarbons (V (C₅)) is preferably less than 5 vol. % in view of a high power generation quantity per CO₂ emission.

The content of hydrocarbon compounds having a carbon number of 6 is not particularly limited, however, the content of hydrocarbon compounds having a carbon number of 6 based on the total content of hydrocarbons (V (C₆)) is preferably less than 10 vol. % in view of a high power generation quantity per CO₂ emission.

Incidentally, the above-described V (C₄), V (C₅), V (C₆), V (C₇+C₈), and V (C₁₀₊) are values quantitatively measured by the following gas chromatography. That is, these values are measured in conditions: employing capillary columns of methyl silicon for columns; using helium or nitrogen as a carrier gas; employing a hydrogen ionization detector (FID) as a detector; the column length of 25 to 50 m; the carrier gas flow rate of 0.5 to 1.5 ml/min, the split ratio of (1:50) to (1:250); the injection inlet temperature of 150 to 250° C.; the initial column temperature of −10 to 10° C.; the final column temperature of 150 to 250° C., and the detector temperature of 150 to 25° C.

Further, the distillation properties according to the second aspect of the present invention are as follows:

The initial boiling point (initial boiling point 0) in distillation is over 40° C. and 100° C. or lower, preferably 50° C. or higher, and more preferably 60° C. or higher. The 10 vol. % distillation temperature (T₁₀) is over 50° C. and 120° C. or lower, preferably 60° C. or higher. The 90 vol. % distillation temperature (T₉₀) is 110° C. or higher and 180° C. or lower, preferably 170° C. or lower, and more preferably 160° C. or lower. The final boiling point in distillation is 130° C. or higher and 210° C. or lower, preferably 190° C. or lower, more preferably 170° C. or lower.

If the initial boiling point (initial boiling point 0) in distillation is low, the fuel is highly inflammable and an evaporative gas (THC) is easy to be generated and there is a problem to handle the fuel. Similarly regarding to the 10 vol. % distillation temperature (T₁₀), if it is less than the above-described restricted value, the fuel is highly inflammable and an evaporative gas (THC) is easy to be generated and there is a problem to handle the fuel.

On the other hand, the upper limit values of the 90 vol. % distillation temperature (T₉₀) and the final boiling point in distillation are determined in view of a high power generation quantity per weight, a high power generation quantity per CO₂ emission, a low fuel consumption of a fuel cell system as a whole, a low THC in an exhaust gas, short starting time of a system, small deterioration of a reforming catalyst to retain the initial properties, and the like.

Further, the 30 vol. % distillation temperature (T₃₀), 50 vol. % distillation temperature (T₅₀), and 70 vol. % distillation temperature (T₇₀) of the fuel of the invention are not particularly restricted, however, the 30 vol. % distillation temperature (T₃₀) is preferably 80° C. or higher and 140° C. or lower, the 50 vol. % distillation temperature (T₅₀) is preferably 70° C. or higher and 120° C. or lower, and the 70 vol. % distillation temperature (T₇₀) is 90° C. or higher and 150° C. or lower.

Incidentally, the above-described initial boiling point (initial boiling point 0) in distillation, the 10 vol. % distillation temperature (T₁₀), the 30 vol. % distillation temperature (T₃₀), the 50 vol. % distillation temperature (T₅₀), the 70 vol. % distillation temperature (T₇₀), the 90 vol. % distillation temperature (T₉₀), and the final boiling point in distillation are distillation properties measured by JIS K 2254, “Petroleum products-Determination of distillation characteristics”.

Further, the content of sulfur in a fuel of the invention is not particularly restricted, however, because deterioration of a fuel cell system comprising a reforming catalyst, a water gas shift reaction catalyst, a carbon monoxide removal catalyst, fuel cell stacks, and the like can be suppressed to low and the initial performances can be maintained for a long duration, the content is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, further more preferably 10 ppm by mass or less, much further more preferably 1 ppm by mass or less, and most preferably 0.1 ppm by mass or less.

Here, sulfur means sulfur measured by JIS K 2541, “Crude Oil and Petroleum Products-Determination of sulfur content”, in case of 1 ppm by mass or more and means sulfur measured by ASTM D4045-96, “Standard Test Method for Sulfur in Petroleum Products by Hydrogenolysis and Rateometric Colorimetry” in the case of less than 1 ppm by mass.

In the invention, the respective contents of saturates, olefins and aromatics are not particularly restricted, however, based on the whole hydrocarbons, saturates (V (S)), olefins (V (O)) and aromatics (V (Ar)) are preferably 30 vol. % or more, 35 vol. % or less, and 50 vol. % or less, respectively. Hereinafter, these components will separately be described.

In view of a high power generation quantity per weight, a high power generation quantity per CO₂ emission, a low fuel consumption of a fuel cell system as a whole, small THC in an exhaust gas, and a short starting time of the system, V (S) is preferably 30 vol. % or more, more preferably 40 vol. % or more, further more preferably 50 vol. % or more, much further more preferably 60 vol. % or more, much further more preferably 70 vol. % or more, much further more preferably 80 vol. % or more, much further more preferably 90 vol. % or more, and most preferably 95 vol. % or more.

In view of a high power generation quantity per weight, a high power generation quantity per CO₂ emission, small deterioration of a reforming catalyst to maintain the initial performances for a long duration, and a good storage stability, V (O) is preferably 35 vol. % or less based on the whole hydrocarbons, more preferably 25 vol. % or less, further more preferably 20 vol. % or less, much further more preferably 15 vol. % or less, and most preferably 10 vol. % or less.

In view of a high power generation quantity per weight, a high power generation quantity per CO₂ emission, a low fuel consumption of a fuel cell system as a whole, small THC in an exhaust gas, a short starting time of the system, and small deterioration of a reforming catalyst to maintain the initial performances for a long duration, V (Ar) is preferably 50 vol. % or less, more preferably 45 vol. % or less, further more preferably 40 vol. % or less, much further more preferably 35 vol. % or less, much further more preferably 30 vol. % or less, much further more preferably 20 vol. % or less, much further more preferably 10 vol. % or less, and most preferably 5 vol. % or less.

Further, it is most preferable to satisfy the above-described preferable ranges of sulfur and the above-described preferable ranges for aromatics since deterioration of a reforming catalyst can be suppressed to low and the initial performances can be maintained for a long duration.

The values of the above-described V (S), V (O), and V (Ar) are all measured value according to the fluorescent indicator adsorption method of JIS K 2536, “Liquid petroleum products-Testing method of components”.

Further, in the invention, the ratio of paraffins in saturates of a fuel is not particularly restricted, however, in view of a high H₂ generation quantity, a high power generation quantity per weight and a high power generation quantity per CO₂ emission, the ratio of paraffins in saturates is preferably 60 vol. % or more, more preferably 65 vol. % or more, further more preferably 70 vol. % or more, much further more preferably 80 vol. % or more, much further more preferably 85 vol. % or more, much further more preferably 90 vol. % or more, and most preferably 95 vol. % or more.

The above-described saturates and paraffins are values quantitatively measured by the following gas chromatography.

Further, the ratio of branched paraffins in the above-described paraffins is not particularly restricted, however, the ratio of branched paraffins in paraffins is preferably 30 vol. % or more, more preferably 50 vol. % or more, and most preferably 70 vol. % or more in view of a high power generation quantity per weight, a high power generation quantity per CO₂ emission, a low fuel consumption of a fuel cell system as a whole, small THC in an exhaust gas, and a short starting time of the system.

The amounts of the above-described paraffins and branched paraffins are values quantitatively measured by the above-described gas chromatography.

Further, in the invention, the heat capacity of a fuel is not particularly restricted, however, the heat capacity is preferably 2.6 kJ/kg·° C. or less at 15° C. and 1 atm in liquid phase in view of a low fuel consumption of a fuel cell system as a whole.

Further, in the invention, the heat of vaporization of a fuel is not particularly restricted, however, the heat of vaporization is preferably 400 kJ/kg or less in view of a low fuel consumption of a fuel cell system as a whole.

Those heat capacity and heat of vaporization can be calculated from the contents of respective components quantitatively measured by the above-described gas chromatography and from the numeric values per unit weight of the respective components disclosed in “Technical Data Book-Petroleum Refining”, Vol. 1, Chap. 1, General Data, Table 1C1.

Further, in the invention, the Reid vapor pressure (RVP) of a fuel is not particularly restricted, however, it is preferably 10 kPa or more in view of the power generation quantity per weight and preferably less than 100 kPa in view of suppression of the amount of an evaporative gas (evapo-emission). It is more preferably 10 kPa or more and less than 80 kPa, further more preferably 10 kPa or more and less than 60 kPa. Here, the Reid vapor pressure (RVP) means the vapor pressure (Reid vapor pressure (RVP)) measured by JIS K 2258, “Testing Method for Vapor Pressure of Crude Oil and Products (Reid Method)”.

Further, in the invention, research octane number (RON, the octane number by research method) is not particularly restricted, however, it is preferably 101.0 or less in view of a high power generation quantity per weight, a low fuel consumption of a fuel cell system as a whole, small THC in an exhaust gas, a short starting time of the system and small deterioration of a reforming catalyst to maintain the initial performances for a long duration. Here, the research octane number (RON) means the research method octane number measured by JIS K 2280, “Petroleum products-Fuels-Determination of octane number, cetane number and calculation of cetane index”.

Further, in the invention, the oxidation stability of a fuel is not particularly restricted, however, it is preferably 240 minutes or longer in view of storage stability. Here, the oxidation stability is the oxidation stability measured according to JIS K 2287, “Testing Method for Oxidation Stability of Gasoline (Induction Period Method)”.

Further, in the invention, the density of a fuel is not particularly restricted, however, it is preferably 0.78 g/cm³ or less in view of a high power generation quantity per weight, a low fuel consumption of a fuel cell system as a whole, small THC in an exhaust gas, a short starting time of the system and small deterioration of a reforming catalyst to maintain the initial performances for a long duration. Here, the density means the density measured according to JIS K 2249, “Crude petroleum and petroleum products-Determination of density and petroleum measurement tables based on a reference temperature (15° C.)”.

A method of producing the fuel according to the present invention is not particularly limited. For example, one or at least two kinds of oxygenates and hydrocarbons are mixed to produce the fuel.

For example, the fuel can be prepared by blending one or more following hydrocarbon base materials; light naphtha obtained by the atmospheric distillation of crude oil, heavy naphtha obtained by the atmospheric distillation of crude oil, desulfurized light naphtha obtained by desulfurization of light naphtha, desulfurized heavy naphtha obtained by desulfurization of heavy naphtha, isomerate obtained by converting light naphtha into isoparaffins by an isomerization process, alkylate obtained by the addition reaction (alkylation) of low molecule weight olefins to hydrocarbons such as isobutane, desulfurized alkylate obtained by desulfurizing alkylate, low sulfur alkylate produced from desulfurized hydrocarbons such as isobutane and desulfurized low molecule weight olefins, reformate obtained by catalytic reforming, raffinate which is residue after extraction of aromatics from distillate of reformate, light distillate of reformate, middle to heavy distillate of reformate, heavy distillate of reformate, cracked gasoline obtained by by catalytic cracking or hydrocracking process, light distillate of cracked gasoline, heavy distillate of cracked gasoline, desulfurized cracked gasoline obtained by desulfurizing cracked gasoline, desulfurized light distillate of cracked gasoline obtained by desulfurizing light distillate of cracked gasoline, desulfurized heavy distillate of cracked gasoline obtained by desulfurizing heavy distillate of cracked gasoline, light distillate of “GTL (Gas to Liquids)” obtained by F-T (Fischer-Tropsch) synthesis after cracking natural gas or the like to carbon monoxide and hydrogen, desulfurized LPG obtained by desulfurizing LPG, and the like. The fuel can also be produced by desulfurizing by hydrotreating or adsorption after mixing one or more types of the above base materials.

Among them, preferable materials as the base materials for the production of the fuel of the invention are light naphtha, desulfurized light naphtha, isomerate, desulfurized alkylates obtained by desulfurizing alkylates, low sulfur alkylates produced from desulfurized hydrocarbons such as isobutane and desulfurized low molecule weight olefins, desulfurized light distillate of cracked gasoline obtained by desulfurizing a light distillate of cracked gasoline, a light distillate of GTL, desulfurized LPG obtained by desulfurizing LPG, and the like.

A fuel for a fuel cell system of the invention may comprise additives such as dyes for identification, oxidation inhibitors for improvement of oxidation stability, metal deactivators, corrosion inhibitors for corrosion prevention, detergents for keeping cleanness of a fuel system, lubricity improvers for improvement of lubricating property and the like.

However, since a reforming catalyst is to be scarcely deteriorated and the initial performances are to be maintained for a long duration, the amount of the dyes is preferably 10 ppm or less and more preferably 5 ppm or less. For the same reasons, the amount of the oxidation inhibitors is preferably 300 ppm or less, more preferably 200 ppm or less, further more preferably 100 ppm or less, and most preferably 10 ppm or less. For the same reasons, the amount of the metal deactivators is preferably 50 ppm or less, more preferably 30 ppm or less, further more preferably 10 ppm or less, and most preferably 5 ppm or less. Further, similarly since a reforming catalyst is to be scarcely deteriorated and the initial performances are to be maintained for a long duration, the amount of the corrosion inhibitors is preferably 50 ppm or less, more preferably 30 ppm or less, further more preferably 10 ppm or less, and most preferably 5 ppm or less. For the same reasons, the amount of the detergents is preferably 300 ppm or less, more preferably 200 ppm or less, and most preferably 100 ppm or less. For the same reasons, the amount of the lubricity improvers is preferably 300 ppm or less, more preferably 200 ppm or less, and most preferably 100 ppm or less.

A fuel of the invention is to be employed as a fuel for a fuel cell system. A fuel cell system mentioned herein comprises a reformer for a fuel, a carbon monoxide conversion apparatus, fuel cells and the like, however, a fuel of the invention may be suitable for any fuel cell system.

The reformer for a fuel is an apparatus for obtaining hydrogen, which is a fuel of fuel cells, by reforming a fuel. Practical examples of the reformer are:

-   (1) a steam reforming type reformer for obtaining products of mainly     hydrogen by treating a heated and vaporized fuel and steam with a     catalyst such as copper, nickel, platinum, ruthenium and the like; -   (2) a partial oxidation type reformer for obtaining products of     mainly hydrogen by treating a heated and vaporized fuel and air with     or without a catalyst such as copper, nickel, platinum, ruthenium     and the like; and -   (3) an auto-thermal reforming type reformer for obtaining products     of mainly hydrogen by treating a heated and vaporized fuel, steam     and air, which carries out the partial oxidation of (2) in the prior     stage and carries out the steam type reforming of (1) in the     posterior stage while using the generated heat of the partial     oxidation reaction with a catalyst such as copper, nickel, platinum,     ruthenium and the like.

The carbon monoxide conversion apparatus is an apparatus for removing carbon monoxide which is contained in a gas produced by the above-described reformer and becomes a catalyst poison in a fuel cell and practical examples thereof are:

-   (1) a water gas shift reactor for obtaining carbon dioxide and     hydrogen as products from carbon monoxide and steam by reacting a     reformed gas and steam in the presence of a catalyst of such as     copper, nickel, platinum, ruthenium and the like; and -   (2) a preferential oxidation reactor for converting carbon monoxide     into carbon dioxide by reacting a reformed gas and compressed air in     the presence of a catalyst of such as platinum, ruthenium and the     like, and these are used singly or jointly.

As a fuel cell, practical examples are a proton exchange membrane fuel cell (PEFC), a phosphoric acid type fuel cell (PAFC), a molten carbonate type fuel cell (MCFC), a solid oxide type fuel cell (SOFC) and the like.

Further, the above-described fuel cell system can be employed for an electric automobile, a hybrid automobile comprising a conventional engine and electric power, a portable power source, a dispersion type power source, a power source for domestic use, a cogeneration system and the like.

EXAMPLES

The properties of base materials employed for the respective fuels for examples and comparative examples are shown in Table 1.

Also, the properties of the respective fuels employed for examples and comparative examples are shown in Table 2.

TABLE 1 desulfurized full- desulfurized range heavy sulfolane naphtha naphtha raffinate alkylate *1 *2 *3 *4 sulfur 0.3 0.2 0.4 8 hydrocarbon carbon number: C₄ vol. % 1.6 0.0 0.7 8.6 ratio carbon number: C₅ vol. % 12.5 0.3 4.4 3.2 carbon number: C₆ vol. % 19.7 7.2 46.2 2.8 carbon number: C₇ vol. % 20.9 28.1 47.6 2.5 carbon number: C₈ vol. % 24.3 33.1 1.1 79.8 carbon number: C₇ + C₈ vol. % 45.2 61.2 48.7 82.3 carbon number: C₉ vol. % 18.5 26.4 0.0 1.1 carbon number: C₁₀₊ vol. % 2.5 4.9 0.0 2.0 composition saturates vol. % 92.8 91.7 95.5 99.8 olefins vol. % 0.6 0.0 4.4 0.1 aromatics vol. % 6.6 8.3 0.1 0.1 paraffins in saturates vol. % 85.5 79.0 98.2 100.0 branched paraffins in vol. % 44.4 48.6 72.5 91.3 paraffins oxygen mass % 0.0 0.0 0.0 0.0 distillation initial boiling point ° C. 35.0 71.5 66.0 31.0 10% point ° C. 55.0 92.5 72.5 71.5 30% point ° C. 73.5 100.5 75.5 98.5 50% point ° C. 91.5 111.5 79.5 105.5 70% point ° C. 112.5 127.0 86.0 110.0 90% point ° C. 134.5 135.5 98.5 122.5 final boiling point ° C. 155.5 157.5 126.0 181.5 heat capacity (liquid) kJ/kg · ° C. 2.105 2.038 2.155 2.071 heat capacity (gas) kJ/kg · ° C. 1.523 1.506 1.573 1.590 heat of vaporization kJ/kg 317.2 304.2 318.8 289.8 RVP kPa 66.9 19.5 29.9 58.5 research octane number 63.4 53.2 56.9 95.6 oxidation stability min. >1440 >1440 >1440 >1440 density g/cm³ 0.7085 0.7331 0.6821 0.6955 net heat of combustion kJ/kg 44225 43940 44585 44488 low sulfur alkylate *5 MTBE ethanol methanol sulfur 0.1 0.1 0.1 0.1 hydrocarbon carbon number: C₄ vol. % 8.4 — — — ratio carbon number: C₅ vol. % 3.3 — — — carbon number: C₆ vol. % 2.9 — — — carbon number: C₇ vol. % 2.4 — — — carbon number: C₈ vol. % 80.2 — — — carbon number: C₇ + C₈ vol. % 82.6 — — — carbon number: C₉ vol. % 0.9 — — — carbon number: C₁₀₊ vol. % 1.9 — — — composition saturates vol. % 99.7 — — — olefins vol. % 0.2 — — — aromatics vol. % 0.1 — — — paraffins in saturates vol. % 100.0 — — — branched paraffins in vol. % 91.4 — — — paraffins oxygen mass % 0.0 18.2 34.8 49.9 distillation initial boiling point ° C. 30.5 55.0 78.0 64.7 10% point ° C. 71.0 — — — 30% point ° C. 99.0 — — — 50% point ° C. 105.0 — — — 70% point ° C. 110.5 — — — 90% point ° C. 121.5 — — — final boiling point ° C. 177.0 — — — heat capacity (liquid) kJ/kg · ° C. 2.071 2.075 2.339 2.456 heat capacity (gas) kJ/kg · ° C. 1.594 1.477 1.381 1.343 heat of vaporization kJ/kg 290.8 319.7 855.6 1096.8 RVP kPa 59.5 53.0 15.9 30.0 research octane number 95.4 118.0 130.0 110.0 oxidation stability min. >1440 — — — density g/cm³ 0.6951 0.7456 0.7963 0.7961 net heat of combustion kJ/kg 44501 35171 26824 19916 *1: those obtained by desulfurization of naphtha fractions obtained by distillation of crude oil *2: heavy components obtained by further distilling desulfurized full-range naphtha *3: remaining fractions left after extracting aromatics from reformate with a sulforane process *4: gasoline fractions obtained by treating butane, butene fractions with an alkylation process *5: gasoline fractions obtained by treating desulfurized butane, butene fractions with an alkylation process

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Mixing desulfurized heavy naphtha 95% ratio desulfurized full-range naphtha alkylate 85% low sulfur alkylate 85% sulfolane raffinate 91% methanol  5% ethanol  9% MTBE 15% 15% Properties Sulfur ppm by mass 0.2 6.7 0.4 0.1 ratio by carbon number vol. % carbon number: C₄ 0.0 8.6 0.7 8.4 carbon number: C₅ vol. % 0.3 3.2 4.4 3.3 carbon number: C₆ vol. % 7.2 2.8 46.2 2.9 carbon number: C₇ vol. % 28.1 2.5 47.6 2.4 carbon number: C₈ vol. % 33.1 79.8 1.1 80.2 carbon number: C₇ + C₈ vol. % 61.2 82.3 48.7 82.6 carbon number: C₉ vol. % 26.4 1.1 0.0 0.9 carbon number: C₁₀₊ vol. % 4.9 2.0 0.0 1.9 Composition saturates vol. % 91.7 99.8 95.5 99.7 olefins vol. % 0.0 0.1 4.4 0.2 aromatics vol. % 8.3 0.1 0.1 0.1 paraffins in saturates vol. % 79.0 100.0 98.2 100.0 branched paraffins in vol. % 48.6 91.3 72.5 91.4 paraffins Oxygen mass % 2.7 2.9 3.6 2.9 Density g/cm³ 0.7363 0.7030 0.6924 0.7027 Distillation properties initial boiling point ° C. 60.5 32.5 60.5 32.0 10% point ° C. 82.5 55.0 69.5 54.0 30% point ° C. 92.5 89.5 72.5 89.0 50% point ° C. 104.0 99.0 78.0 98.0 70% point ° C. 120.5 106.5 83.5 106.0 90% point ° C. 131.0 120.0 97.5 118.0 final boiling point ° C. 155.0 195.0 124.0 190.0 Reid vapor pressure kPa 41 57 39 58 Research octane number 58.9 98.9 62.0 99.1 Oxidation stability min. 1440 or 1440 or 1440 or 1440 or more more more more Net heat of combustion kJ/kg 42640 43006 42746 43020 Heat capacity (liquid) kJ/kg · ° C. 2.060 2.072 2.174 2.072 Heat capacity (gas) kJ/kg · ° C. 1.497 1.572 1.553 1.575 Heat of vaporization kJ/kg 347.0 294.6 374.4 295.4 Comp. Ex. 1 Comp. Ex. 2 Mixing desulfurized heavy naphtha 100% ratio desulfurized full-range naphtha 10% alkylate low sulfur alkylate sulfolane raffinate methanol 90% ethanol MTBE Properties Sulfur ppm by mass 0.2 0.1 ratio by carbon number carbon number: C₄ vol. % 0.0 1.6 carbon number: C₅ vol. % 0.3 12.5 carbon number: C₆ vol. % 7.2 19.7 carbon number: C₇ vol. % 28.1 20.9 carbon number: C₈ vol. % 33.1 24.3 carbon number: C₇ + C₈ vol. % 61.2 45.2 carbon number: C₉ vol. % 26.4 18.5 carbon number: C₁₀₊ vol. % 4.9 2.5 Composition saturates vol. % 91.7 92.8 olefins vol. % 0.0 0.0 aromatics vol. % 8.3 6.6 paraffins in saturates vol. % 79.0 85.5 branched paraffins in vol. % 48.6 44.4 paraffins Oxygen mass % 0.0 45.4 Density g/cm³ 0.7331 0.7873 Distillation properties initial boiling point ° C. 71.5 35.0 10% point ° C. 92.5 55.0 30% point ° C. 100.5 64.5 50% point ° C. 111.5 65.0 70% point ° C. 127.0 65.5 90% point ° C. 135.5 72.5 final boiling point ° C. 157.5 125.5 Reid vapor pressure kPa 19 — Research octane number 53.2 — Oxidation stability min. 1310 1440 or more Net heat of combustion kJ/kg 43940 22103 Heat capacity (liquid) kJ/kg · ° C. 2.038 2.424 Heat capacity (gas) kJ/kg · ° C. 1.506 1.359 Heat of vaporization kJ/kg 304.2 1026.7

These respective fuels were subjected to a fuel cell system evaluation test, an evaporative gas test, and a storage stability test.

Fuel Cell System Evaluation Test

(1) Steam Reforming

A fuel and water were evaporated by electric heating and led to a reformer filled with a noble metal type catalyst and kept at a prescribed temperature by an electric heater to generate a reformed gas enriched with hydrogen.

The temperature of the reformer was adjusted to be the minimum temperature (the minimum temperature at which no THC was contained in a reformed gas) at which reforming was completely carried out in an initial stage of the test.

Together with steam, a reformed gas was led to a carbon monoxide conversion apparatus (a water gas shift reaction) to convert carbon monoxide in the reformed gas to carbon dioxide and then the produced gas was led to a solid polymer type fuel cell to carry out power generation.

A flow chart of a steam reforming type fuel cell system employed for the evaluation was illustrated in FIG. 1.

(2) Partial Oxidation

A fuel is evaporated by electric heating and together with air, the evaporated fuel was led to a reformer filled with a noble metal type catalyst and kept at a 1100° C. by an electric heater to generate a reformed gas enriched with hydrogen.

Together with steam, a reformed gas was led to a carbon monoxide conversion apparatus (a water gas shift reaction) to convert carbon monoxide in the reformed gas to carbon dioxide and then the produced gas was led to a solid polymer type fuel cell to carry out power generation.

A flow chart of a partial oxidation type fuel cell system employed for the evaluation was illustrated in FIG. 2.

(3) Evaluation Method

The amounts of H₂, CO, CO₂ and THC in the reformed gas generated from a reformer were measured immediately after starting of the evaluation test. Similarly, the amounts of H₂, CO, CO₂ and THC in the reformed gas generated from a carbon monoxide conversion apparatus were measured immediately after starting of the evaluation test.

The power generation quantity, the fuel consumption, and the CO₂ amount emitted out of a fuel cell were measured immediately after starting of the evaluation test and 100 hours later from the starting.

The energy (preheating energy) necessary to heat the respective fuels to a prescribed reforming temperature were calculated from the heat capacities and the heat of vaporization.

Further, these measured values, calculated values and the net heat of combustion of respective fuels were employed for calculation of the performance deterioration ratio of a reforming catalyst (the power generation amount after 100 hours later from the starting divided by the power generation amount immediately after the starting), the thermal efficiency (the power generation amount immediately after the starting divided by the net heat of combustion of a fuel), and the preheating energy ratio (preheating energy divided by the power generation amount).

Evaporative Gas Test

A hose for filling a sample was attached to a fuel supply port of a 20 liter portable gasoline can and the installation part was completely sealed. While an air venting valve of the can being opened, 5 liter of each fuel was loaded. On completion of the loading, the air venting valve was closed and the can was left still for 30 minutes. After the can being kept still, an activated carbon adsorption apparatus was attached to the air venting valve and the valve was opened. Immediately, 10 liter of each fuel was supplied from the fuel supply port. After 5 minutes of the fuel supply, while the air venting valve being opened and kept as it was, the vapor was absorbed in the activated carbon and after that, the weight increase of the activated carbon was measured. Incidentally, the test was carried out at a constant temperature of 25° C.

Storage Stability Test

A pressure resistant closed container was filled with each fuel and oxygen, heated to 100° C. and while the temperature being kept as it was, the container was kept still for 24 hours. Evaluation was carried out according to “Petroleum products-Motor gasoline and aviation fuels-Determination of washed existent gum” defined as JIS K 2261.

The respective measured values and the calculated values are shown in Table 3.

TABLE 3 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Evaluation results Electric power generation by steam reforming method (reforming temperature = optimum reforming temperature 1)) Optimum ° C. 600 590 580 590 reforming temperature Electric energy kJ/fuel kg initial 28990 29280 29190 29290 performance 100 hours 28960 29220 29170 29280 later performance 100 hours 0.10% 0.20% 0.07% 0.03% deterioration later ratio Thermal efficiency 2) initial 68% 68% 68% 68% performance CO₂ generation kg/fuel kg initial 3.019 2.985 2.953 2.984 performance Energy per CO₂ KJ/CO₂-kg initial 9603 9809 9885 9816 performance Preheating kJ/fuel kg 1255 1219 1271 1221 energy 3) Preheating 4.3% 4.2% 4.4% 4.2% energy ratio 4) Electric power generation by partial oxidation reforming method (reforming temperature 1100° C.) Electric energy kJ/fuel kg initial 13930 14380 14460 14400 performance 100 hours 13910 14350 14440 14390 later performance 100 hours 0.14% 0.21% 0.14% 0.07% deterioration later ratio Thermal efficiency 2) initial 33% 33% 34% 33% performance CO₂ generation kg/fuel kg initial 3.021 2.987 2.953 2.985 performance Energy per CO₂ KJ/CO₂-kg initial 4611 4814 4897 4824 performance Preheating kJ/fuel kg 2003 2021 2078 2025 energy 3) Preheating 14.4% 14.1% 14.4% 14.1% energy ratio 4) Evaporative gas test Evaporative gas g/test 11.3 4.7 7.1 4.8 Storage stability test Washed existent mg/100 ml 2 2 2 1 gum Comp. Ex. 1 Comp. Ex. 2 Evaluation results Electric power generation by steam reforming method (reforming temperature = optimum reforming temperature 1)) Optimum ° C. 670 460 reforming temperature Electric energy kJ/fuel kg initial 29670 18280 performance 100 hours 29650 18270 later performance 100 hours 0.07% 0.05% deterioration later ratio Thermal efficiency 2) initial 68% 83% performance CO₂ generation kg/fuel kg initial 3.113 1.529 performance Energy per CO₂ KJ/CO₂-kg initial 9531 11956 performance Preheating kJ/fuel kg 1321 1663 energy 3) Preheating 4.5% 9.1% energy ratio 4) Electric power generation by partial oxidation reforming method (reforming temperature 1100° C.) Electric energy kJ/fuel kg initial 14130 10650 performance 100 hours 14110 10640 later performance 100 hours 0.14% 0.09% deterioration later ratio Thermal efficiency 2) initial 32% 48% performance CO₂ generation kg/fuel kg initial 3.115 1.530 performance Energy per CO₂ KJ/CO₂-kg initial 4536 6961 performance Preheating kJ/fuel kg 1969 2533 energy 3) Preheating 13.9% 23.8% energy ratio 4) Evaporative gas test Evaporative gas g/test 4.1 8.1 Storage stability test Washed existent mg/100 ml 2 1 gum 1) the minimum temperature at which no THC is contained in a reformed gas 2) electric energy/net heat of combustion of fuel 3) energy necessary for heating a fuel to a reforming temperature 4) preheating energy/electric energy

INDUSTRIAL APPLICABILITY

As described above, a fuel for a fuel cell system of the invention comprising oxygenates in the specific amount has performances with small deterioration and can provide high output of electric energy, and further the fuel can satisfy a variety of performances for a fuel cell system. 

1. A fuel for a fuel cell system, which comprises at least 5 vol. % of hydrocarbons based on the whole fuel and 0.5 to 20 mass % of oxygenates in terms of an oxygen content based on the whole fuel, wherein the total content of hydrocarbon compounds which have carbon numbers of 7 and 8 is 20 vol. % or more based on the whole hydrocarbons and the total content of hydrocarbon compounds which have carbon numbers of 10 or more is 20 vol. % or less based on the whole hydrocarbons, a sulfur content is 50 ppm by mass or less based on the whole fuel, saturates are 30 vol. % or more, olefins are 35 vol. % or less and aromatics are 50 vol. % or less based on the whole hydrocarbons, respectively, and the fuel has distillation properties of the initial boiling point in distillation of 32° C. or higher and 100° C. or lower, the 10 vol. % distillation temperature of over 50° C. and 120° C. or lower, the 90 vol. % distillation temperature of 97.5° C. or higher and 180° C. or lower, and the final boiling point in distillation of 124° C. or higher and 210° C. or lower.
 2. A fuel for a fuel cell system according to claim 1, wherein a ratio of paraffins in saturates is 60 vol. % or more.
 3. A fuel for a fuel cell system according to claim 2, wherein a ratio of branched paraffins in paraffins is 30 vol. % or more.
 4. A fuel for a fuel cell system according to claim 1, wherein heat capacity of the fuel is 2.6 kJ/kg° C. or less at 15° C. and 1 atm in liquid phase.
 5. A fuel for a fuel cell system according to claim 1, wherein heat of vaporization of the fuel is 400 kJ/kg or less.
 6. A fuel for a fuel cell system according to claim 1, wherein Reid vapor pressure of the fuel is 10 kPa or more and less than 100 kPa.
 7. A fuel for a fuel cell system according to claim 1, wherein research octane number of the fuel is 101.0 or less.
 8. A fuel for a fuel cell system according to claim 1, wherein oxidation stability of the fuel is 240 minutes or longer.
 9. A fuel for a fuel cell system according to claim 1, wherein density of the fuel is 0.78 g/cm³ or less. 